Network telemetry system and method

ABSTRACT

A telemetry system produces, transmits and receives signal sets from network nodes, which correspond to transceiver stations. Repeater scheduling and other interference mitigating techniques are utilized to simultaneously transmit from multiple nodes with minimized network degradation. Update interval/rate and network throughput are thereby fixed regardless of the number of network nodes and a network telemetry method is provided using the system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority in U.S. Provisional Application No. 61/800,063 for Increased Throughput Downhole Network Telemetry System and Method, filed Mar. 15, 2013. This application is related to U.S. Patent Applications Ser. No. 61/731,898 for Downhole Low Rate Linear Repeater Network Timing Control System and Method, filed Nov. 30, 2012; and Ser. No. 61/799,588, for Robust Network Downhole Telemetry Repeater System and Method, filed Mar. 15, 2013. All of the above applications are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to telemetry apparatuses and methods, and more particularly to acoustic telemetry increased throughput network systems and methods for the well construction (drilling, completion) and production (e.g., oil and gas) industries.

2. Description of the Related Art

Acoustic telemetry is a method of communication used in the well drilling, completion and production industries. In a typical drilling environment, acoustic extensional carrier waves from an acoustic telemetry device are modulated in order to carry information via the drillpipe as the transmission medium to the surface. Upon arrival at the surface, the waves are detected, decoded and displayed in order that drillers, geologists and others helping steer or control the well are provided with drilling and formation data. In production wells, downhole information can similarly be transmitted via the well casings.

The theory of acoustic telemetry as applied to communication along drillstrings has generally been confirmed by empirical data in the form of accurate measurements. It is now generally recognized that the nearly regular periodic structure of drillpipe imposes a passband/stopband structure on the frequency response, similar to that of a comb filter. Dispersion, phase non-linearity and frequency-dependent attenuation make drillpipe a challenging medium for telemetry, the situation being made even more challenging by the significant surface and downhole noise generally experienced.

Drillstring acoustic telemetry systems are commonly designed with multiple transceiver nodes located at spaced intervals along the drillstring or wellbore. The nodes can be configured as signal repeaters as necessary. Acoustic telemetry networks can function in a synchronized fashion with the operation of the nodes and repeater nodes and other system components. Data packets consisting of downhole sensor data were relayed node to node, in a daisy chain or linear fashion, typically beginning from a node located in the borehole apparatus (BHA), through the network to a destination, usually the surface receiver system. For purposes of minimizing interference between nodes, the data packets were transmitted (typically up-string) using time division multiplexing (TDM) techniques. Maximizing data packet transmission speed and throughput are objectives of drillstring telemetry systems and methods. For a discussion of a repeater network for these applications, see co-pending U.S. Patent Application Ser. No. 61/731,898.

When exploring for oil or gas, and in other drilling applications, an acoustic transmitter can be placed near the BHA, typically near the drill bit where the transmitter can gather certain drilling, wellbore, and geological formation data, process this data, and then convert the data into a signal to be transmitted uphole to an appropriate receiving and decoding station. In some systems, the transmitter is designed to produce elastic extensional stress waves that propagate through the drillstring to the surface, where the waves are detected by sensors, such as accelerometers, attached to the drillstring or associated drilling rig equipment. These waves carry information of value to the drillers and others who are responsible for steering the well. Examples of such systems and their components are shown in: Drumheller U.S. Pat. No. 5,128,901 for Acoustic Data Transmission through a Drillstring; Drumheller U.S. Pat. No. 6,791,470 for Reducing Injection Loss in Drillstrings; Camwell et al. U.S. Pat. No. 7,928,861 for Telemetry Wave Detection Apparatus and Method; and Camwell et al. U.S. Pat. No. 8,115,651 for Drill String Telemetry Methods and Apparatus. These patents are incorporated herein by reference.

SUMMARY OF THE INVENTION

In the practice of the present invention, a network is configured with multiple nodes using the acoustic transmission channel simultaneously, i.e., “multiplexing” the channel. Network throughput is thus decoupled from the number of nodes and performance increases accordingly. Internode interference can be controlled by one or more methods, including the following:

-   -   Node transmission timing: nodes transmitting at separate times.         Current (prior art) method which tends to be relatively         inefficient. E.g., time division multiplexing (TDM).     -   Attenuation where nodes transmit at the same time and         interference is suppressed by differences in propagation         distance and associated path loss (signal attenuation).     -   Frequency differentiation where nodes transmit simultaneously on         different frequencies whereby interference is suppressed by the         frequency separations and associated filtering.     -   Signal orthogonality with nodes transmitting at the same time         but interference being suppressed by the orthogonal relationship         of the signal sets.     -   Directional transmitter and receiver configurations, with nodes         tuned to transmit in the direction of the desired destination         node or receive in the direction of the originating node,         thereby minimizing interference within the network.

Other objects and advantages of the present invention will be apparent from the following description. Detailed descriptions of exemplary embodiments are provided in the following sections. However, the invention is not limited to such embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram of a typical drilling rig, which can include an acoustic telemetry system with a downhole serial network embodying an aspect of the present invention.

FIG. 2 is a fragmentary, side-elevational and cross-sectional view of a typical drillstring, which can provide the medium for acoustic telemetry transmissions for the present invention.

FIG. 3 is a schematic diagram of a prior art linear network timing control system with nodes transmitting sequentially at different times, following a time division multiplexing (TDM) approach

FIG. 4 is a schematic diagram of a path loss attenuation isolation system with a two-node gap transmission schedule.

FIG. 5 is a schematic diagram of a path loss attenuation isolation system with a one-node gap transmission schedule.

FIG. 6 is a schematic diagram of a path loss attenuation isolation system wherein nodes transmit and receive simultaneously.

FIG. 7 is a schematic diagram of a configuration whereby a node is adapting a filter to estimate the channel between the node's transmitter and receiver.

FIG. 8 is a schematic diagram showing receiver signal isolation from the transmitter signal.

FIG. 9 is a schematic diagram of an increased-rate linear telemetry network scheduling system using orthogonal signal sets.

FIG. 10 is a schematic diagram of another increased rate linear telemetry network scheduling system using orthogonal signal sets combined with simultaneous transmission and reception.

FIG. 11 is a schematic diagram showing an example of multi-node transmission in an along-string measurement (ASM) configuration with varying/accumulating node payloads.

FIG. 12 is a schematic diagram illustrating a node receiving a portion of a desired signal transmission during an interference-free period.

FIG. 13 is a schematic diagram showing a system using directional transceivers to suppress intra-node interference and increase network throughput.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, reference is made to “up” and “down” waves, but this is merely for convenience and clarity. It is to be understood that the present invention is not to be limited in this manner to conceptually simple applications in acoustic communication from the downhole end of the drillstring to the surface.

I. Drilling Rig, Drillstring and Well Environment

Referring to the drawings in more detail, the reference numeral 2 generally designates a high throughput network system embodying an aspect of the present invention. Without limitation on the generality of useful applications of the system 2, an exemplary application is in a drilling rig 4 (FIG. 1). For example, the rig 4 can include a derrick 6 suspending a traveling block 8 mounting a kelly swivel 10, which receives drilling mud via a kelly hose 11 for pumping downhole into a drillstring 12. The drillstring 12 is rotated by a kelly spinner 14 connected to a kelly pipe 16, which in turn connects to multiple drill pipe sections 18, which are interconnected by tool joints 19, thus forming a drillstring of considerable length, e.g., several kilometers, which can be guided downwardly and/or laterally using well-known techniques.

The drillstring 12 can terminate at or near a bottom-hole (borehole) apparatus (BHA) 20, which can be at or near an acoustic transceiver node (Primary) Station 0 (ST0). Other rig configurations can likewise employ the present invention, including top-drive, coiled tubing, etc. FIG. 1 also shows the components of the drillstring 12 just above the BHA 20, which can include, without limitation, a repeater transceiver node 26 (ST1) and an additional repeater transceiver node 22 (ST2). An upper, adjacent drillpipe section 18 a is connected to the repeater 22 and the transmitter 26. A downhole adjacent drillpipe section 18 b is connected to the transmitter 26 and the BHA 20. A surface receiver node 21 is located at the top of the drillstring 12 and is adapted for receiving the acoustic telemetry signals from the system 2 for further processing, e.g., by a processor or other output device for data analysis, recording, monitoring, displaying and other functions associated with a drilling operation.

FIG. 2 shows the internal construction of the drillstring 12, e.g., an inner drillpipe 30 within an outer casing 32. Interfaces 28 a, 28 b are provided for connecting drillpipe sections to each other and to the other drillpipe components, as described above. W.1 illustrates an acoustic, electromagnetic or other energy waveform transmitted along the drillstring 12, either upwardly, downwardly, or laterally (in the case of horizontal wells). The drillstring 12 can include multiple additional repeater transceiver nodes 22 at intervals determined by operating parameters such as optimizing signal transmission and reception with minimal delays and errors. The drillstring 12 can also include multiple sensors along its length for producing output signals corresponding to various downhole conditions.

Data packets contain sensor or node status data and are transmitted from the primary node (e.g., ST0, typically the deepest node) and relayed from node-to-node in a daisy-chain (herein interchangeably referred to also as linear or serial) fashion to the surface receiver (Surface Rx) 21, which is generally located at or near the wellhead. The data packets include sensor measurements from the BHA 20 and other sensors along the drillstring 12. Such data packet sensor measurements can include, without limitation, wellbore conditions (e.g., annular/bore/differential pressure, fluid flow, vibration, rotation, etc.). Local sensor data can be added to the data packet being relayed at each sensor node, thus providing along-string-measurements (ASMs).

A single node functions as the master node (e.g., ST0) and is typically an edge node at the top or bottom of the drillstring 12. The master node monitors well conditions and sends data packets of varying type and intervals accordingly.

II. Prior Art Acoustic Repeater Scheduling

FIG. 3 shows the operation of a prior art linear telemetry network scheduling configuration where node transmissions are scheduled for separate non-overlapping time windows in order to prevent inter-node interference and the associated degradation in link performance (reliability and range). This constitutes time division multiplexing (TDM) channel management. However, the update interval increases with the number of nodes, whereby the network throughput decreases. For example, with a five-node, 20 bits per second (bps) transmission link rate system, neglecting guard and signal propagation times, the effective data rate (network throughput) is approximately (20 bps)/(5 nodes)=4 bps, while in a 2 node network, the network throughput is approximately (20 bps)/(2 nodes)=10 bps.

III. Multiplexing Acoustic Transmission Channels

Preferably multiple nodes are configured for using the acoustic transmission channels at the same time, i.e., “multiplexing” the drillstring channel. Multiplexing, with multiple nodes transmitting simultaneously, decouples network throughput dependency on the number of nodes, and increases performance. However, if not mitigated, multiple nodes transmitting simultaneously will lead to inter-node interference and an associated degradation in link performance. One or more of the following methods can be implemented to control internode interference during multi-node transmission:

-   -   Signal attenuation, with nodes transmitting simultaneously and         interference being suppressed by differences in propagation         distance and associated path loss, and perhaps further optimized         through adjustment of node transmission power level.     -   Frequency separation with nodes transmitting simultaneously but         on different frequencies whereby interference is suppressed.     -   Signal orthogonality, with nodes transmitting at the same time         and interference being suppressed by low correlation between         signals within allowable signal set.     -   Directional transmitter and receiver configurations, with nodes         tuned to transmit in the direction of the desired destination         node or receive in the direction of the originating node,         thereby minimizing interference within the network.

IV. Isolation Via Path Loss Attenuation

FIG. 4 shows a 2-node gap multiplexing scheduling configuration. Interfering transmissions are mitigated by physical separation (e.g., 2-node gap). This configuration is applicable to electromagnetic pulse systems as well as acoustic, and is further applicable to downlink, uplink and bi-directional networks. Interfering transmissions are mitigated by physical separation and associated signal propagation path loss: 3-link propagation path loss attenuation (desired) versus 1-link propagation path loss attenuation (interference). Additional interference minimization can be achieved through adjustment of the transmitter output power levels to minimize interference at one location, while providing sufficient signal power at the desired node receiver. Update interval/rate and network throughput are thus fixed regardless of the number of network nodes. Only latency increases with node number.

The interference between nodes can be further managed by coordinating network timing in such a manner that, while multiple node transmissions overlap in time, the desired signal precedes the anticipated interferer signal such that a sufficient portion of the desired signal experiences no interference allowing the receiving node to achieve more reliable signal detection, timing and phase recovery, and decoding once the interfering node begins transmission and signals overlap. This method allows the receiver to favour the desired signal over the interferer. See, e.g., FIG. 12, which is discussed below.

FIG. 5 shows a 1-node gap multiplexing scheduling configuration wherein multiple nodes are transmitting at the same time. This configuration is more aggressive than the 2-node gap configuration shown in FIG. 4, having less interference suppression. Interfering transmissions are mitigated by physical separation and associated path loss: 1-link path loss attenuation (desired) versus 2-link path loss attenuation (interference). Update interval/rate and network throughput are thus fixed regardless of the number of network nodes. Only latency increases with node number.

FIG. 6 shows scheduling with an update rate which can be fixed at approximately 2t_(tx), for example, regardless of the number of nodes. Only latency increases with node number. The receiver must be able to operate during self-transmission, without being excessively degraded by self-interference. This can be accomplished by assigning non-interfering frequency or orthogonal signal sets to the transmitter and receiver. If the transmitter and a receiver operate in the same channel (time, frequency), or further interference suppression is desired, high-power interfering self-transmission signals can be isolated from received signals through channel estimation techniques, as described below.

FIG. 7 shows a “receive-while-transmitting” configuration wherein an estimating function with a feedback loop is used to estimate the in-node transmitter to receiver channel. A transmitter (e.g., a piezo-electric stack, in the case of acoustics) to receiver (accelerometer, in the case of acoustics) channel estimation is shown, using an adaptive filter to emulate the intra-node channel. FIG. 8 shows how the estimated intra-node channel can be used to suppress self-interference. Specifically, by applying an estimated channel filter to the known transmitted signal (as derived in FIG. 7), to translate the signal to how the receiver would perceive it, and subtracting it from the composite receive signal (self-interference from transmitter+desired receive signal originating from another node) to provide output corresponding to the desired receive signal only.

FIG. 9 shows an increased rate repeater scheduling configuration assigning orthogonal (i.e., low-interference) signal sets (indicated by α, β) to transmitter and receiver nodes, thereby allowing multiple signals in respective channels simultaneously, increasing the update rate and the effective data rate. The signal sets can be reused once interference nodes are sufficiently separated to ensure adequate interference isolation. The update interval, t_(update), is fixed at ˜2t_(tx), regardless of the number of repeaters and only latency increases. The concept is the application of orthogonal multiple access techniques to increase channel efficiency (e.g., CDMA—Code Domain Multiple Access, FDMA—Frequency Domain Multiple Access, OFDM —Orthogonal Frequency Domain Multiplexing, etc.) as an alternative to the relatively inefficient TDM (Time Division Multiplexing) methods.

Examples of low-interference signal sets include: signals of non-overlapping frequencies (Frequency Division Multiplexing (FDM)), which can be contiguous frequency blocks (e.g., different passbands) or interleaved blocks (e.g., OFDM); signals of low cross-correlations, such as up/down, linear/exponential chirps, pseudorandom noise (PRN) sequences (Code Division Multiplexing (CDM)), e.g., Walsh codes, Hadamard, etc.; and signals transmitted on separate, isolated mediums (channels): acoustic, electromagnetic pulse, and mud pulse (MP); and propagation modes (e.g., axial, longitudinal and spiral).

FIG. 10 shows orthogonal signal sets combined with simultaneous transmit and receive, to providing an update rate, t_(update), fixed at ˜t_(tx), regardless of the number of nodes whereby only latency increases with node number. Node receivers are able to operate during transmission with minimized intra-node (self) interference due to transmitter-receiver signal orthognality, as previously discussed. If the transmitter and the receiver operate in the same channel, high-power interfering self-transmission signals can be isolated from received signals through channel estimation techniques, as described below.

FIG. 11 is a schematic diagram showing an example of an along-string measurement (ASM) configuration with varying/accumulating node payloads and signal propagation interference isolation.

FIG. 12 shows signal transmission scheduling refinement whereby a desired transmission (e.g., from M2 T_(x) to M2 R_(x)) precedes an interfering transmission (e.g., from M1 T_(x) to M2 R_(x)), creating a short period of interference-free reception of the desired signal. This interference-free period improves signal detection, timing and phase recovery, effectively allowing the receiver (e.g., M2 R_(x)) to “lock” onto the desired signal, and generally improve link robustness.

FIG. 13 shows a system with directional transceivers for interference suppression. The node receivers are tuned to receive upwardly-traveling signals and to suppress/reject downwardly-traveling signals. This can be accomplished by equipping an acoustic node with multiple transmitters and receivers, and phasing their outputs such that directional transmission or reception is achieved (e.g., transmissions propagate only uphole and receivers only detect signals originating from downhole, and vice-versa). The details of such an operation would be known to one versed in antenna beam forming techniques, and as such will not be elaborated in this text. Receive and transmit directionality can be exploited together, or individually, to suppress interference between nodes, enabling multiple nodes to transmit at the same time. Remaining interference is separated by a two-node gap.

The configurations described above have advantages of preserving multi-hop repeater network throughput, which is fundamentally related to channel multiplexing (reuse) efficiency. Multiple nodes must share the channel, reducing system throughput proportionally to the number of nodes in a system. For example, a five-node system capable of 40 bits-per-second (bps) has a maximum throughput of only 40 bps/5 nodes=8 bps, neglecting guard and signal propagation times, while a two-node system has a maximum throughput of 40 bps/2 nodes=20 bps. All multi-hop linear telemetry systems will encounter the same limitation, including electromagnetic (EM) systems.

It is to be understood that the invention can be embodied and combined in various forms, and is not to be limited to the examples discussed above. The range of components and configurations which can be utilized in the practice of the present invention is virtually unlimited. 

1. A wireless telemetry network system, which includes: multiple network nodes; a sensor associated with one or more of said nodes and adapted for providing output comprising signal data corresponding to an operating or status condition; a transmitter associated with one of said nodes for propagating said signal data between nodes; a receiver associated with one of said nodes for receiving signals from other nodes; multiple network nodes adapted for receiving said signal data; and said system being adapted for transmitting telemetry signals across multiple network links simultaneously.
 2. A linear wireless telemetry network system for a well including a wellbore structure extending subsurface downwardly from the surface, which telemetry network system includes: multiple network nodes distributed along the wellbore; at least one said node including a sensor adapted for providing a signal data set output corresponding to a downhole condition; a transmitter for propagating said signal between nodes; a receiver for receiving said signal from other nodes; and said system being adapted for transmitting telemetry signals across multiple network links simultaneously.
 3. The telemetry system according to claim 2, which includes: said telemetry signals being chosen from among the group comprising acoustic, electromagnetic (EM), mud pulse (MP) and optical.
 4. The telemetry system according to claim 2 wherein said signal sets comprise orthogonal (low interference/cross-correlation) signal sets assigned to network nodes so as to reduce interference at adjacent nodes.
 5. The telemetry system according to claim 4 wherein said telemetry signals are located in multiple, minimally-interfering frequency channels within a medium and/or separate mediums chosen from among the group comprising acoustic, EM and MP.
 6. The telemetry system according to claim 2 wherein: said nodes have predefined separations (and therefore a signal propagation associated attenuation level) and/or transmission power levels adapted so as to maintain interference at receiver locations within a tolerable range.
 7. The telemetry system according to claim 6, which includes: an update interval rate and network throughput being fixed regardless of the number of network nodes.
 8. The telemetry system according to claim 2, which includes: a respective node including a transmitter and a receiver; and the respective node simultaneously transmitting and receiving.
 9. The telemetry system according to claim 8, which includes a filter adapted to an approximation of the channel between the respective node's transmitter and receiver.
 10. The telemetry system according to claim 8, which includes said receiver being adapted for receiving with mitigated self-interference during transmission.
 11. The telemetry system according to claim 9, which includes an estimation function including: a transmitter-to-receiver intranode channel providing an output; said adaptive filter having the signal destined for transmission as a reference input; a summer receiving outputs from said receiver channel and said adaptive filter; said summer providing an error signal as a feedback output to said adaptive filter; and said adaptive filter being adjusted so as to minimize error signal.
 12. The telemetry system according to claim 9, which includes a receiver signal isolation function including: an estimated intranode transmitter-to-receiver channel filter having the signal destined for transmission as an input from the transmitter and providing an output that is the estimated transmitter signal as perceived by the receiver; a summer receiving inputs from said adaptive filter and the receiver signal output that are synchronized in time; and said summer providing an output comprising the received signal with reduced transmitter signal content.
 13. The telemetry system according to claim 2, which includes: said transmitter and said receiver operating in the same channel; said received signals being isolated from each other; said receiver being configured to receive with minimized self-interference during transmission; and said control system including a function for favoring a desired signal over an interferer signal.
 14. The telemetry system according to claim 2 which includes: said control system function coordinating network timing whereby a desired signal precedes in time an anticipated, overlapping interferer signal creating an interference-free time period at a node for reception of a portion of the desired signal, thereby allowing the node receiver to lock onto the desired signal.
 15. The telemetry system according to claim 2, which includes: multiple receivers within a node with signal outputs which are phased and combined in such a manner to form a phased array that gives rise to directional discrimination of incoming signals to minimize interference from an undesired node transmissions arriving from another direction.
 16. The telemetry system according to claim 2, which includes: multiple transmitters within a node with output signals phased in such a manner so as to propagate outgoing signals in one direction only and minimizing interference at another node.
 17. The telemetry system according to claim 2, which includes: said directional receivers being adapted to suppress undesired interfering signals arriving at the receiver from one direction, while receiving desired signals from another direction.
 18. A method of transmitting acoustic telemetry signals in a well including a wellbore structure extending subsurface downwardly from the surface, which method includes the steps of: defining with said structure a linear/daisy-chain network; providing multiple network nodes positioned along said structure; transmitting said signals in signal sets comprising orthogonal (low interference) signal sets assigned to network nodes to reduce inter-node interference; pre-defining node separations and/or transmission power levels; predefining tolerable interference ranges for said receivers; maintaining interference at receiver locations within tolerable, predefined ranges through signal propagation attenuation; providing a sensor associated with one or more of said nodes and adapted for providing output comprising signal data corresponding to an operating, status, or wellbore condition; providing a transmitter associated with one of said nodes for propagating said signal data between nodes; providing a receiver associated with one of said nodes; receiving with said receiver signals from other nodes; receiving said signal data with said multiple network nodes; and transmitting telemetry signals across multiple network links simultaneously.
 19. The method according to claim 18, which includes the additional step of: providing said well with a node located at said surface and a bottom hole assembly (BHA) located at the bottom of said well; providing sensors configured to monitor operating conditions near or at the BHA; generating said signals with data corresponding to said BHA operating stations; transmitting said BHA operating condition data signals to said surface node; and exporting said BHA operating condition data signals to a remote data processing system configured to monitor operating conditions at said well.
 20. The method according to claim 18, which includes the additional step of generating said telemetry signals using a signal type chosen from among the group comprising: acoustic; electromagnetic (EM); mud pulse (MP); and optical. 